(1) Field of the Invention
The invention relates to refrigeration liquids that are dyed such that they cause a readily visible stain in the event of a leak in the refrigeration system in which they are used. More particularly, it relates to the use of 1,4-bis(2-methyl-6-ethylanilino)anthraquinone or some of its closely similar homologs as dyes in refrigeration liquids composed essentially of a volatile halocarbon refrigerant and a relatively non-volatile oil serving as a lubricant for the refrigeration apparatus or other vapor compression heat transfer mechanism in which the composition is used. Still more particularly, the invention relates to refrigeration liquids containing an anthraquinone dye that is deep blue in color, that is substantially soluble in the halocarbon as well as the lubricating oil constituting the refrigeration composition, and that has a high degree of stability at the high temperatures and in the chemical environment encountered in a mechanical refrigeration cycle. The invention likewise relates to the use of such dyed refrigeration liquids in a refrigeration process wherein the presence of a stable dye is capable of serving as a conspicuous leak indicator in the event of a leak occurring in the course of a long period of operation.
(2) The State of the Art
It has been known in the art to use various dyes to indicate the occurrence and location of leaks in mechanical refrigeration systems employing refrigerants composed of mixtures of fluorocarbons and a refrigeration oil. For instance, U.S. Pat. No. 3,370,013 describes such a refrigerant composition using an azo dye or a mixture of azo dyes as a leak indicator. Other dyes were proposed previously in U.S. Pat. No. 1,915,965 for a similar purpose. More recently, the use of certain anthraquinone dyes has been proposed for this purpose in U.S. Pat. No. 3,770,640.
However, previously proposed dyes have suffered from one or more disadvantages, notably in terms of insufficient chemical or thermal stability, insufficient solubility in the particular refrigerant composition for which they were intended, relatively complex molecular structure and consequent difficulty in manufacturing them, or unsatisfactory color. Obviously, unless the selected dye is sufficiently soluble both in the volatile halocarbon and in the relatively non-volatile refrigeration oil, leakage of the refrigerant composition containing such a dye will produce an oil stain of insufficient intensity for ready detection.
Proper chemical and thermal stability are particularly important because insufficiently stable dyes gradually change or lose color and may produce a precipitate, thereby losing effectiveness as a leak indicator and impairing the operation of the refrigeration mechanism.
In addition, to yield a commercially acceptable refrigeration composition, the dye (1) must be such as to permit the stains that result in the location of a leak to be easily and essentially completely removed by a solvent such as perchloroethylene, methylene chloride or trichlorofluoromethane; (2) must not cause a significant increase in the pour point of the refrigeration oil; (3) must not have any significant adverse effect on the various materials used in refrigeration apparatus; e.g., elastomeric gaskets, cotton sleeving, mechanical parts made of polyester or nylon; (4) must have no adverse effect on the dielectric strength of the refrigation oil; and (5) must not raise the floc point of the oil.
Adequate solubility of the dye in the halocarbon-containing refrigerant composition as well as the refrigeration oil used in formulating it is of course of major importance. More particularly, it is important that the dye be capable of being dissolved in the refrigerant composition in a sufficient concentration to produce the desired intensely colored stain in the event of a leak without precipitating from the composition as it passes through the various evaporation and compression stages of the refrigeration cycle. And it is particularly important that the solubility of the dye in the relatively non-volatile refrigeration oil be sufficiently high to produce an intensely colored oil stain when the dye-containing composition leaks from the system and the halocarbon refrigerant evaporates, causing the dye present to concentrate in the oil that remains.
Last, but not least, many manufacturers or operators of commercial refrigeration, freezer or air conditioning units or heat pumps insist on using refrigerant compositions that possess an intense blue color, in preference to some other color such as green or red, in order to be able to differentiate a refrigerant leak from a leak of some other fluid in the system; e.g., red motor fuel or hydraulic fluid under the hood of a motor vehicle. The requirement that the dye be blue has further greatly increased the difficulty of finding a dye meeting all the specified requirements.
A narrow class of anthraquinone dyes having a particular characteristic structure has now been found which meets all of the specified requirements in a surprisingly effective manner.